When the steel material for the cavity is selected depending on the type of plastic resin and the functions expected of the molded product.
　If the selection of the steel is not appropriate, it may not be possible to polish the fined surface into a fine surface, or corrosion may progress during the molding, or the wearing out may occur at a fast rate.
　The table below shows the major types of plastic resins or the guidelines for selecting the recommendation of steel.